DAERA Management Notes: Dairying

Trevor Alcorn

Sire selection: Selecting bulls from an AI catalogue or for natural service is one of the most important decisions you can take as a dairy farmer.

Why – because it will significantly influence the type of cows you will have milking in five years time. Your decision on breeding replacements should not be taken lightly. Base it on your answers to the following two questions:

l What type of system and cows do you want in five years?

As a general guide, bulls chosen from an AI catalogue should have a high £PLI of over £400. However there will be considerable variation between these bulls with some having high milk production potential (PTA Milk of over 700) while others will exhibit excellent milk quality (PTA BF% and PR% over 0.10), fertility (PTA Fertility over 12.0), lifespan (PTA Lifespan over 0.5) or a combination of these. Consider what traits or range of traits is important to you. Bulls suited to a completely housed system will not suit someone who is spring calving or wants to make the most from grazed grass.

l What is the current genetic merit of my herd?

Information on genetic merit is available to pedigree registered herds through their breed society or milk recorder. For non-pedigree herds that milk record the same information is available for each cow if her sire is identified and a herd genetic summary will be available.

However, for herds that don’t milk, record assessing genetic merit is more difficult but as a general guide each cow has half the genetic merit of her sire. For example, a cow sired by Oman (O-Bee Manfred Justice) who has PTAs of 445 for milk, 0.06 for BF% and 0.08 for PR% will have a PTA of 222 for milk, 0.03 for BF% and 0.04 for PR%.

Bull selection

Based on your answers to the two questions; select bulls with one or more of the following traits that will rectify current areas of weakness in your herd and meet future plans.

l PTA Fertility typically ranges from -15 to +15 and bulls with higher figures have better fertility. Each one point increase in Fertility Index, for example from 2 to 3 is predicted to decrease calving interval by 0.5 days and increase non-return rates by 0.5%.

l PTA Lifespan is expressed in terms of lactations and takes account of the main reasons cows are culled from a herd - infertility, lameness and mastitis. It typically ranges from -0.5 to +0.5 and bulls with positive PTA Lifespan should increase progeny longevity. For example, daughters from a +0.5 bull are predicted to survive, on average, 0.5 lactations longer than those from a bull with a PTA of zero.

l PTA SCC is expressed as a percentage and typically ranges from -30 to +30. Bulls with a negative PTA SCC should reduce future heifer SCC with each 1% change in a sire’s SCC PTA predicted to change his daughters SCC by 1%. For example, the SCC of daughters from a bull with a PTA SCC of -10% will be 10% lower than daughters from a bull with a PTA SCC of zero. Due to the strong link between SCC and mastitis SCC PTA will also reduce mastitis incidence.

There are about 850 Holstein bulls available in the United Kingdom across the range of AI companies. An excellent tool is available on the AHDB Breeding+ website to filter the list of bulls according to the specific selection criteria of your herd. The tool can be accessed at http://bit.ly/2f6G2E7